Add the chicken stock to a microwave-safe liquid measuring cup and microwave on high power for 3 minutes, until hot. Stir in the saffron threads and set aside.

On a cutting board, pat the shrimp dry with paper towels. Season with 1 teaspoon of salt and the pepper on both sides and set aside.

Heat the olive oil in a 12-inch (30 cm) cast-iron skillet over medium-high heat until it begins to shimmer. Add the chorizo and cook, stirring, until browned in spots, 3 minutes. Add the onion and cook until softened, about 3 minutes. Add the garlic and paprika and cook, stirring, until aromatic, about 30 seconds. Add the rice and stir until lightly toasted, 1 minute.

Add the tomatoes and reserved chicken stock and stir to combine. Reduce the heat to low and cover the pan with a lid. Cook without stirring until the rice is al dente, 15 minutes.

Remove the lid and arrange the shrimp, mussels, and peas on top of the rice. Cover and increase the heat to medium-high. Cook until the shrimp are opaque and the mussels are open, 5 minutes. Discard any mussels that do not open.

Remove the lid and pour the lemon juice over the paella. Sprinkle with the remaining teaspoon of salt and the parsley and serve.

Enjoy!